1. Field of the Invention
The present invention relates to a switch with pre-alarm means for alarming that abnormal current flows on breaker of the switch previous to tripping operation of the breaker, and especially relates to a switch with pre-alarm means having self-holding function for alarming that an abnormal current flew even when the abnormal current had disappeared.
2. Description of the Prior Art
Conventionally, a switch with pre-alarm means having an operation indicator and pre-alarm apparatus is known in the art. The operation indicator is, for example, a light emitted diode (LED) or a buzzer and provided on an outer face of a housing of the switch.
When accident happens on the load, abnormal over current flows on breaker of the switch. The pre-alarm apparatus detects the over current. When level of the over current is above a predetermined alarming level, the pre-alarm apparatus outputs a signal for lighting the LED or for driving the buzzer. Thereby, the user or operator confirms the occurrence of the over current by vision or hearing.
After lapse of a predetermined time period under occurrence of the over current, the breaker of the switch is tripped and the over current is cut off.
However, when the level of the abnormal over current once becomes below the predetermined alarming level, the LED puts off and the operator or user can not confirm the occurence of the over current. Therefore, the conventional switch with pre-alarm means has disadvantage that the operation indicator must be monitored all times.